Method of manufacturing negative electrode

Abstract

Disclosed is a method of manufacturing a negative electrode, wherein a negative electrode structure is electrochemically charged while being pressed with a plurality of pre-lithiation rolls in performing pre-lithiation of the negative electrode structure by a roll-to-roll method, and here, the pressing pressures of the plurality of pre-lithiation rolls are increased in a movement direction of the negative electrode structure. Since the pressing pressures are increased in the movement direction of the negative electrode structure, volume expansion, structural deformation, and damage to an active material due to the pre-lithiation may be prevented, and at the same time, the pre-lithiation may be performed uniformly, and thus it is preferable for improving lifespan characteristics of a negative electrode.

The invention claimed is: 
     
       1. A method of manufacturing a negative electrode, the method comprising:
 preparing a negative electrode roll on which a negative electrode structure is wound, wherein the negative electrode structure comprising a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector; 
 preparing a pre-lithiation bath comprising a pre-lithiation solution, wherein the pre-lithiation bath is sequentially partitioned into an impregnation section, a pre-lithiation section, and an aging section; 
 impregnating the negative electrode structure with the pre-lithiation solution while unwinding the negative electrode structure from the negative electrode roll and moving the negative electrode structure through the impregnation section; 
 pre-lithiating the negative electrode structure while moving the negative electrode structure out of the impregnation section and moving the negative electrode structure through the pre-lithiation section; and 
 aging the negative electrode structure while moving the negative electrode structure out of the pre-lithiation section and moving the negative electrode structure through the aging section, 
 wherein the pre-lithiating of the negative electrode structure comprises: 
 (a) arranging a plurality of pre-lithiation rolls, wherein each roll is rotatable and comprises a core, a lithium metal layer formed on the core, and a separator layer formed on the lithium metal layer, in the pre-lithiation section in a movement direction of the negative electrode structure, and 
 (b) pre-lithiating the negative electrode structure by electrochemically charging the negative electrode structure while moving the negative electrode structure through the pre-lithiation section, wherein the negative electrode active material layer is in contact with the plurality of pre-lithiation rolls, and pressing the negative electrode structure with the plurality of pre-lithiation rolls, and 
 wherein the pressing pressures of the pre-lithiation rolls in contact with the negative electrode structure are increased as the negative electrode structure moves. 
 
     
     
       2. The method of  claim 1 , wherein the pressing pressures of the pre-lithiation rolls in contact with the negative electrode structure are proportionally increased as the negative electrode structure moves. 
     
     
       3. The method of  claim 1 , wherein the pressing pressures of the plurality of pre-lithiation rolls are in a range of 5 kg/cm to 1,600 kg/cm. 
     
     
       4. The method of  claim 1 , wherein the pressing pressures of the pre-lithiation rolls are in a range of 5 kg/cm to 180 kg/cm when the negative electrode structure enters the pre-lithiation section, and
 the pressing pressures of the pre-lithiation rolls are in a range of 40 kg/cm to 1,600 kg/cm when the negative electrode structure is passing through the pre-lithiation section. 
 
     
     
       5. The method of  claim 1 , wherein differences between the pressing pressures of the pre-lithiation rolls when the negative electrode structure enters the pre-lithiation section and the pressing pressures of the pre-lithiation rolls when the negative electrode structure is passing through the pre-lithiation section are in a range of 15 kg/cm to 1,500 kg/cm. 
     
     
       6. The method of  claim 1 , wherein a time for the negative electrode structure to move through the pre-lithiation section is in a range of 5 minutes to 120 minutes. 
     
     
       7. The method of  claim 1 , wherein a time for the negative electrode structure to move through the aging section is 0.5 times to 21 times a time for the negative electrode structure to move through the pre-lithiation section. 
     
     
       8. The method of  claim 1 , wherein a time for the negative electrode structure to move through the impregnation section is 1 time to 10 times a time for the negative electrode structure to move through the pre-lithiation section. 
     
     
       9. The method of  claim 1 , wherein a temperature of the pre-lithiation bath is in a range of 10° C. to 80° C. 
     
     
       10. The method of  claim 1 , further comprising washing the aged negative electrode structure by taking the aged negative electrode structure out of the pre-lithiation bath, introducing the aged negative electrode structure into a washing bath comprising an organic solvent, and moving the aged negative electrode structure through the washing bath. 
     
     
       11. The method of  claim 10 , wherein a time for the aged negative electrode structure to move through the washing bath is 0.1 times to 5 times a time for the negative electrode structure to move through the pre-lithiation section. 
     
     
       12. The method of  claim 10 , further comprising drying the washed negative electrode structure. 
     
     
       13. The method of  claim 12 , wherein a time to dry the washed negative electrode structure is 0.1 times to 5 times a time for the negative electrode structure to move through the pre-lithiation section. 
     
     
       14. The method of  claim 1 , wherein
 the negative electrode active material layer comprises a negative electrode active material, and 
 the negative electrode active material comprises one or more selected from the group consisting of a carbon-based active material and a silicon-based active material.